An excellent site for buying maps:
http://www.omnimap.comI have been searching maps for Dominican Republic for a long time, and here I found maps in scale 1:50.000 covering the entirely country. Maps can be bought both as paper maps and scanned in 300dpi. It is not clear that you can buy them scanned, but you can. Email them before ordering telling that you want them scanned. Price per map is US$ 20, and they cover about 25X20km. When you place the order shipping is added, but you will not be charged for it.
The maps are not calibrated so you have to do it yourself.